1. Field of the Invention
The present invention relates in general to a jog device for magnetic recording and reproducing apparatus and, more particularly, to a structural improvement in such a jog device for prevention of screen noise caused by either abrupt variation of tape tension or variation of length of the tape running passage in the case of conversion of mode of the apparatus from a normal-direction reproducing mode into a reverse-direction reproducing mode.
2. Description of the Prior Art
With reference to FIG. 1, there is shown magnetic recording and reproducing apparatus having a typical jog device. As shown in this drawing, a power transmission mechanism of the above apparatus includes a capstan motor 19 for rotating a capstan shaft 19b. The capstan motor 19 coupled to the capstan shaft 19b is mounted on the top surface of a base plate 1 at the right side of the base plate 1. Fitted over the capstan shaft 19b above the top surface of the capstan motor 19 is a pulley 19a whose bottom surface comes into close contact with the top surface of the capstan motor 19. A gear pulley 5 is rotatably mounted on a shaft 8a fixed to the base plate 1 about the capstan motor 19. The pulley 5 is connected to the pulley 19a of the capstan motor 19 through a belt 18 wrapped about both the pulleys 5 and 19a. A spring 10a is fitted over the shaft 8a under the gear pulley 5 as shown in FIG. 2. The power transmission mechanism also includes an idler arm 8 whose one end or a boss type end is connected to the shaft 8a of the gear pulley 5 but whose other end or a simple rod type end is connected to an idler shaft 7c. That is, the idler arm 8 is connected to the gear pulley shaft 8a and the idler shaft 7c at its opposed ends respectively, thus to rotatably support the idler 7 that is placed under the gear pulley 5.
As shown in FIG. 2, the idler 7 and the idler arm 8 are connected to each other through a felt 9, a spring 10 and a washer 5a so that a predetermined frictional torque is generated by the felt 9, the spring 10 and the washer 5a in response to rotation of the idler arm 8. In the idler 7, a large idler gear 7a and a small idler gear 7b are integrally fitted over the idler shaft 7c. That is, the idler 7, which includes the small idler gear 7b intending to gear into a clutch gear 13 during a normal speed running mode of the tape and the large idler gear 7a intending to gear into a no-slip drive gear 17 during a FF/REW mode of the tape, is mounted on the rod type end of the idler arm 8 with the felt 9 interposed between the idler 7 and the idler arm 8. The spring 10, which is adapted for biasing the idler 7 toward the idler arm 8 and causing a frictional force to be generated in the felt 9, is supported by the washer 5a which in turn rotatably support the idler 7 on the idler arm 8. The large idler gear 7a always gears into a pulley gear 5b of the gear pulley 5, which gear pulley 5 is rotated by the rotating force of the capstan motor 19 transmitted to the pulley 5 through the belt 18.
As shown in FIG. 1, a clutch 4 is mounted on a shaft 11a fixed to the base plate 1 by the left side of the idler 7. The clutch 4 comprises a reel drive gear 11, a first friction member 12, the clutch gear 13, a second friction member 14, a disc 15, a coil spring 16, the no-slip drive gear 17 directly coupled to the reel drive gear 11, and a slitted washer 17a as shown in FIG. 3. All of the above elements of the clutch 4 are fitted over the shaft 11a in order. That is, the reel drive gear 11 of the clutch 4, which will gear into a tape supply reel gear 2a placed under a tape supply reel assembly 2, is fitted over the shaft 11a at the bottom position. Extending upward from the center of the reel drive gear 11 are a polygonal shaft 11e and a cylindrical shaft 11d. Here, the cylindrical shaft 11d extends from the top of the polygonal shaft 11e upwardly. Fitted over the shaft 11a above the reel drive gear 11 is the clutch gear 13 which will gear into the small idler gear 7b of the idler 7. The first and second friction members 12 and 14 of the hollow disc type are placed on the bottom surface and the top surface of the clutch gear 13 respectively. The center of the clutch gear 13 is provided with a polygonal hole 13e which will receive the polygonal shaft 11e of the reel drive gear 11 therein. The shape of the polygonal hole 13e of the clutch gear 13 corresponds to the outer appearance of the polygonal shaft 11e of the reel drive gear 11. In the same manner, the center of the disc 15 is provided with a polygonal hole 15e. The coil spring 16 is fitted over the cylindrical shaft 11d of the reel drive gear 11 and supported by the no-slip drive gear 17 rotating along with the reel drive gear 11. The coil spring 16 thus biases the disc 15 toward the reel drive gear 11, thus to cause frictional force to be generated in both the first and second friction members 12 and 14. The slitted washer 17a is fitted over the top section of the shaft 11a after fitting the no-slip drive gear 17 over the shaft 11a, thus to retain the predetermined positions of the clutch elements orderly fitted over the shaft 11a.
In the apparatus, the gear pulley 5, the idler arm 8 and the idler 7 constitute a so-called idler mechanism. The idler mechanism is engaged with either the clutch 4 of the tape supply reel assembly 2 or a clutch (not shown) of a tape take-up reel assembly (not shown) in response to rotating direction of the gear pulley 5, thus to drive either the supply reel assembly 2 or the take-up reel assembly. Here, the idler mechanism is driven by the rotating force of a rotational force source such as the capstan motor 19. Here, it should be understood that an additional clutch may be provided in the tape supply reel assembly 2 having the aforementioned clutch 4.
A tape supply reel shaft 2c is fixed to the base plate 1 by the left side of the clutch 4. The tape supply reel gear 2a which is integrally fitted in the tape reel assembly 2, is fitted over the tape supply reel shaft 2c.
Rotatably mounted on a shaft 40c under the supply reel assembly 2 is a power transmission gear 40 having a projection 40a at a predetermined position thereof. A jog gear 36 partially provided with teeth is rotatably mounted on an end of an arm 33 by a pin 34 in the fight side of the power transmission gear 40. The center of the arm 33 is coupled to a lever 37 by a pin 35. The lever 37 which is rotatably mounted on a bracket 30 is provided with a bent portion 37a on the outside edge of the lever 37 by the side of the power transmission gear 40. A stopper 30a for prevention of clockwise rotation of the lever 37 extends from the bracket 30 as shown in FIG. 1. Another stopper 30b for prevention of rotation of the arm 33 is mounted on the bracket 30 so that the stopper 30b comes into contact with the jog gear 36.
One end of the arm 33 is coupled to one end of the lever 37 by a spring 32. In the same manner, the other end of the lever 37 is coupled to a fixture 38a of the bracket 30 by a spring 38. Here, the fixture 38 denotes a portion of the bracket 30 where the spring 38 is coupled to the bracket 30.
The operation of the magnetic recording and reproducing apparatus will be described hereinbelow.
In a PLAY mode or a normal-direction reproducing mode, the capstan motor 19 is rotated counterclockwise so that the counterclockwise rotating force of the capstan motor 19 is transmitted to the gear pulley 5 through the belt 18. At this time, the gear pulley 5 is rotated counterclockwise in the same rotating direction of the capstan motor 19. As a result of counterclockwise rotation of the gear pulley 5, the idler 7 and idler arm 8 are rotated counterclockwise about the shaft 8a, thus to rotate the clutch gear (not shown) of the tape take-up reel clutch and in turn rotate the tape take-up reel (not shown). The take-up reel thus takes up the magnetic tape (not shown) thereon.
In a REVIEW mode, the capstan motor 19 is rotated clockwise so that the clockwise rotating force of the capstan motor 19 is transmitted to the gear pulley 5 through the belt 18. At this time, the gear pulley 5 is rotated clockwise in the same rotating direction of the capstan motor 19. As a result of clockwise rotation of the gear pulley 5, the idler 7 and idler arm 8 are rotated clockwise about the shaft 8a, thus to render the small idler gear 7b of the idler 7 rotating the clutch gear 13 of the tape supply reel clutch 4. The rotating force of the clutch gear 13 is thus transmitted to the reel drive gear 11 with a predetermined rotating torque through the first friction member 12, which friction member 12 is biased toward the reel drive gear 11 by the coil spring 16 and comes into close contact with the reel drive gear 11. The reel drive gear 11 is thus rotated and, as a result, rotates the tape supply reel gear 2a placed under the tape supply reel assembly 2, thus to make the tape supply reel take up the magnetic tape thereon.
In a FF (Fast Forward) mode, the idler arm 8 is descended by an additional conversion member (not shown) so that the small idler gear 7b is disengaged from the clutch gear 13 but the large idler gear 7a gears into a no-slip drive gear 17. The rotating force of the idler 7 is thus transmitted to the no-slip drive gear 17, thus to rotate the no-slip drive gear 17. As a result of rotation of the no-slip drive gear 17, the reel drive gear 11 is rotated so that the rotating force of the reel drive gear 11 is transmitted to the tape supply reel assembly 2 at a high speed with a high rotating torque through neither the first friction member 12 nor the second friction member 14. In the same manner as described for the tape supply reel assembly 2 in the FF mode, the tape take-up reel assembly (not shown) in the FF mode is transmitted with the rotating force of the reel drive gear 11 at the high steep with the high rotating torque.
Hereinbelow, the operation of the jog device for the magnetic recording and reproducing apparatus will be given.
Conventionally, the jog operation is carried out for reproducing a picture simultaneously with moving the picture by one frame in normal direction or in reverse direction in a STILL mode. With the jog device, one picture will be repeatedly reproduced in the STILL mode. The STILL mode means that the capstan motor 19 is stopped during a PLAY mode. In this STILL mode, the idler 7 engages with the clutch gear (not shown) of the tape take-up reel. When a reverse-direction jog operation for reproducing one picture or one frame while moving the picture in the reverse direction is carded out, the capstan motor 19 is somewhat rotated clockwise, thus to clockwise rotate the idler 7 about the idler shaft 7c. However, since the interval between the pictures of the magnetic tape is extremely short, for example, 58 .mu.m, the capstan motor 19 is not sufficiently rotated and this causes the idler 7 to be not precisely engaged with the clutch gear 13 of the clutch 4.
When the reverse-direction jog operation is continued in the above state, the clockwise rotation of the capstan motor 19 is continued, thus to cause the idler 7 to be continuously rotated and, as a result, precisely engaged with the clutch gear 13 of the tape supply reel. The rotating force of the capstan motor 19 is, therefore, precisely transmitted to the tape supply reel assembly 2 so that the tape supply reel takes up the magnetic tape thereon. At this time, the rotation of the capstan motor 19 is continued until the idler 7 has changed its engagement from the tape take-up reel clutch gear (not shown) to the tape supply reel clutch gear 13. The magnetic tape is thus fed continuously. However, as the idler 7 is not engaged with the tape supply reel clutch gear 13 of the tape supply reel, the tape supply reel assembly 2 can not take up the magnetic tape. In this regard, the tension of the tape about the rotary head drum (not shown) is loose so that the head drum can not read out the signals recorded on the tape and this causes the noise to be generated on the picture. In order to combat this problem, the jog gear 36, the arm 33 and the lever 37 are installed by the side of the tape supply reel clutch 4 such that the teeth of the jog gear 36 are selectively engaged with the no-slip drive gear 17. In addition, the power transmission gear 40 having the projection 40a is rotatably mounted on the shaft 40c by the side of the arm 33.
During the reverse-direction jog operation in the STILL mode, in which STILL mode a specific picture is repeatedly reproduced, the capstan motor 19 rotates the power transmission gear 40 clockwise using the rotating force of an additional drive source, for example, a loading motor that provides the rotating force required in moving the elements of the magnetic recording and reproducing apparatus prior to a desired operation of the apparatus, before the capstan motor 19 is rotated clockwise. The projection 40a of the power transmission gear 40 thus pushes the bent portion 37a of the lever 37, so that the lever 37 is turned counterclockwise about the pin 35. As a result of the counterclockwise turning motion of the lever 37, the tension coil spring 32 is tensioned, thus to cause the arm 33 to be rotated counterclockwise about the pin 35. At this time, the teeth of the jog gear 36, which jog gear 36 is rotated along with the arm 33, are engaged with teeth of the no-slip drive gear 17 of the tape supply reel clutch 4. As a result of the counterclockwise rotation of the am 33, the teeth of the jog gear 36 rotate the no-slip drive gear 17 clockwise and in turn rotate the tape supply reel assembly 2 counterclockwise. Hence, the tape supply reel takes up the magnetic tape thereon, thus to cause the tape about the head drum to be tensioned. At this time, the capstan motor 19 is rotated clockwise, so that the tape is unwound from the reel so as to control the tension of the tape about the head dram. When the reverse-direction jog operation is continued, the above procedure is repeated.
When a normal-direction jog operation or a normal-direction reproducing operation is carried out at the above state, the power transmission gear 40 is rotated counterclockwise, thus to cause the projection 40a of the gear 40 to be disengaged from the bent portion 37a of the lever 37. The lever 37 is thus rotated clockwise by the restoring force of the spring 38. The clockwise rotation of the lever 37 causes the arm 33 to be rotated clockwise along with the jog gear 36. Thus, the teeth of the jog gear 36 come into contact with the teeth of the no-slip drive gear 17. However, as the jog gear 36 is rotated counterclockwise about the fixing pin 34, the no-slip drive gear 17 is not rotated.
It has been noted that the above jog device for the magnetic recording and reproducing apparatus has the following problems.
Since the jog gear 36 is directly transmitted with the rotating force of the loading motor (not shown) and directly transmits the rotating force of the loading motor to the tape supply reel assembly 2. In this regard, the rotating torque of the tape supply reel assembly 2 is increased. The typical jog device thus has a problem that the device causes the tape supply reel assembly 2 to take up the tape thereon with high rotating torque. Furthermore, as the typical jog device feeds the magnetic tape using the rotating force of the capstan motor 19 in the reverse-direction jog operation, the tension of the tape about the head drum is continuously increased when repeating such a jog operation several times. Such continuous increase of the tape tension about the head drum causes abrasion of the head, damage of the magnetic tape and sticking of impurities on the head.